Abstract
A carboxylesterase has been purified from the midgut of the silkworm Bombyx mori L. by a combination of ammonium sulphate fractionation, DEAE-cellulose ion-exchange chromatography, Sephacryl S-200 gel-filtration and preparative polyacrylamide gel electrophoresis (PAGE). The homogeneity of the enzyme was established by PAGE, isoelectricfocusing (IEF) and SDS-PAGE. The enzyme consists of two identical subunits with a subunit molecular weight of 72,000. The two subunits are held by non-covalent bonds. Amino acid analysis of the purified enzyme revealed a high content of hydrophobic amino acid residues. It lacks proline and tryptophan residues and free thiol groups. The data from substrate specificity study in conjunction with kinetic parameters indicate the hydrophobic nature of the active site.
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